1. Field of the Invention
This invention relates to systems using interchangeable lenses, and more particularly to current supply systems for automatic focusing interchangeable lenses.
2. Description of the Prior Art
Recently, in the art of range-finder type cameras, mid-priced cameras and like photographic instruments which have objective lenses built into the camera housings, many techniques have recently been developed for automatically adjusting the position of the objective lens in accordance with the signal representing the object distance measured by an auto-focus unit incorporated in the camera. Many articles employing the same are available in the market. Also in the art of photographic systems of single lens reflex cameras and interchangeable lenses, proposals have been made for the automatic focus adjustment of the objective lens. An interchangeable lens carrying a range finding unit, a focusing lens drive motor and a control mechanism within its structure is also known.
The focusing lens of the interchangeable lens mount is connected to be driven by a the motor, the signal from a range finding device and the signal representing the position of the focusing lens are detected, and the motor is driven depending upon the signals to control movement of the focusing lens. Thus, an auto-focus photographic system using such interchangeable lens mount and the camera body, with the interchangeable lens carrying out its own focusing operation without interface with the camera body, necessitates no channels to the various devices and permits the interchangeable lens and the camera body to be designed as products independent of each other. In this case, when the automatic focusing device comprising the range finding means, motor and computer circuit are incorporated in the interchangeable lens mount, it is necessary that an electrical power source therefor, for example, a battery, be also incorporated in the interchangeable lens mounting. However it is not desirable to incorporate a battery of too large capacity in the interchangeable lens.
Also when incorporating the battery or like electrical power source in the interchangeable lens, a problem arises in the design of the structure of the lens barrel, for example, the shape, bulk and size, may adversely affect holding of the camera when shooting.
But with a battery of small capacity, the camera becomes impossible to use, or fast consumption of electrical energy results. These too are undesirable.
A purpose of the present invention is to supply a means for solving the above-described problems. Where the camera has the interchangeable lens along with an automatic winding unit, in general, the automatic winding unit is equipped with an electrical power source portion of large capacity. Therefore, a solution of the above-described problems is achieved by using this electrical power source portion in supplying current to the automatic focusing device in the interchangeable lens.